The wait is nearly over. On Wednesday night in Denver, President Obama and Mitt Romney will finally face off in the first of three presidential debates. Both candidates have been going to somewhat ridiculous lengths to lower expectations — a game Romney appears to be winning, as a majority of Americans tell pollsters they think Obama will come out on top. Still, plenty of prognosticators believe the GOP challenger will rise to the occasion in what could be a do-or-die moment for his campaign. Of course, both Obama and Romney have plenty of experience on the debate stage, and if history is any guide, both are capable of delivering a knockout performance — or totally screwing up. Here, four shining, and not so shining, moments in each candidate's debating past:

OBAMA

1. Obama to Hillary Clinton: You're "likable enough"Obama's charisma proved to be a big asset in his hotly contested race against Hillary Clinton in the 2008 Democratic primary. On the debate stage, his smiles and jokes set him apart from Clinton's more sober, wonkish policy explanations. "Obama's charm fell short," however, in the final debate before New Hampshire's primary, says TIME, when a moderator asked Clinton about voters who were hesitating to back her because they liked Obama more. Obama chimed in, saying, "You're likable enough, Hillary." The "backhanded compliment" backfired, triggering criticism from Clinton supporters that Obama was "cruel and insensitive, and voters handed him a stunning defeat in New Hampshire just a few days later."

2. Who was the first black president?A debate moderator in 2008 asked Obama, who was on his way to becoming the nation's first black president, whether he agreed with novelist Toni Morrison, who said Bill Clinton was America's "first black president." Awkward! But Obama didn't miss a beat, turning the question into "a brief moment of levity in a contentious slug-fest of a debate," said Katharine Q. Seelye at The New York Times. Obama praised former President Clinton's "affinity" with the black community, then cracked up the crowd by saying: "I would have to investigate more, Bill's dancing abilities and some of this other stuff before I accurately judged whether he was, in fact, a brother."

3. Obama zings Hillary and BillIn one of the many heated exchanges during the "unusually acrimonious and personal" primary battle between Obama and Clinton, says The Associated Press, Obama tried to defend comments he had made about Republican ideas and how Ronald Reagan had successfully championed them. Hillary Clinton interrupted him, saying that she had never criticized Obama for what he said about Reagan. "Your husband did," said Obama. "I'm here. He's not," Clinton responded. Obama shot back: "Well, I can't tell who I'm running against sometimes."

4. Obama to McCain on Iraq: "You were wrong"During the 2008 general election, one of the most memorable exchanges between Obama and his Republican rival, Sen. John McCain, centered on the Iraq war, says CNN. McCain, a Vietnam war hero, criticized Obama for having questioned President George W. Bush's troop surge. Obama pounced, saying, "John, you like to pretend like the war started in 2007. You talk about the 'surge,' the war started in 2003." Obama goes on to say that as the war started, McCain had said the war would be "quick and easy," that we "knew where the weapons of mass destruction were," and that we'd be welcomed as liberators. "You were wrong."

ROMNEY

1. Romney's ill-advised on-stage wagerTexas Gov. Rick Perry put Romney on the spot in a 2011 debate, just weeks ahead of the crucial Iowa caucuses. Perry repeated a line he had used before in the battle over who had the most anti-ObamaCare cred, accusing Romney of having supported an individual mandate to obtain health-insurance coverage when he was governor of Massachusetts. Romney argued that he had never done so, challenging Perry to a $10,000 bet to settle the matter. Huge mistake, said Chris Cillizza at The Washington Post. Romney's suggestion that such a huge sum was the stuff of a friendly wager reinforced the narrative "that his wealth makes him out of touch with the economic concerns of average folks."

2. Mitt's hands-on debate approachIn a particularly testy exchange at a debate in Las Vegas, Rick Perry said it was the "height of hypocrisy" for Romney to claim he would be tough on illegal immigrants when he had hired undocumented workers at his own home. Romney tried to counter the charge by saying Perry's facts were wrong, and by pointing out that Perry's offer of in-state tuition for illegal immigrants at Texas public universities was "a magnet" to encourage them to enter the U.S. Perry interrupted. Finally, Romney put his hand on Perry's shoulder to get him to stop talking. Eventually, Perry let Romney finish. "If the Shoulder Touch on the Strip had occurred in a Las Vegas bar," said Robin Abcarian at the Los Angeles Times, "it might have had a different, perhaps bloodier, outcome."

3. Romney's problems with "illegals" surface... againPerry had a knack for getting the best, or worst, out of Romney. In another back-and-forth over illegal immigrants working at Romney's house, Mitt explained that he had gone to a company that was doing a project for him and said, "look, you can't have any illegals working on our property. I'm running for office, for Pete's sake, I can't have illegals." Sometimes its hard to square the candidate on stage with the real person underneath, says Jonathan Chait at New York, but this "one delicious, authentic moment" was an instant classic because it offered ammunition to critics looking to paint Romney as a calculating elitist.

4. Romney's 2008 opponents accuse him of flip-flopperySome of the GOP primary debates in 2008 seemed more like a "four-on-one gang fight, with Romney as the target," said Holly Bailey at The Daily Beast. His rivals for the Republican nomination hammered him, again and again, for changing his positions on issues from abortion to health care to gay rights. The jabs got a lot of laughs. In a New Hampshire debate, McCain summed up the attacks, telling Romney, "I agree, you are the candidate of the change."